Helicopter wings and other aircraft structures with boundary layer control



May 26, 1953 ASTALKER 2,639,874 HELICOPTER WINGSAND OTHER AIRCRAFTSTRUCTURES WITH BOUNDARY LAYER CONTROL Filed Sept. 10, 1948 2Sheets-Sheet 1 INV TOR. 48 ammfia unv'es mime f p v 4 FIG. 4

y 6, 1953 E. A. STALKER 2,639,874

HELICOPTER WINGS AND OTHER AIRCRAFT STRUCTURES WITH BOUNDARY LAYERCONTROL Filed Sept. 10, 1948' 2 Sheets-Sheet 2 INVENTOR.

5101x901 i aircraft.

Patented May 26, 1953 prism HELICORTER WINGS AND. OTHER AIRCRAFT almsand iir ei i rl ferifi N wh r Win eme 1 v l 4' z "n; Fig. 4 shoe/s a higly'c mbered ving section (taken along imam- 12" irfeitiii Fi roi 'f'ii)ri h-er v s ewffiei n sesi e e l f af with Fig. 6 shows the wing seetionof J Fig. 5 vvith an additional slot atth'e Fi i t ejwlr 1 tailflaps clepressed.' eaw se; v.r i l Presets en he wi s uri .e me

Fig. 9 shows a fuselage with speciallgcal cqnwe tQ., .cluQe. l1G,-a

Fi 0 i a axi se ienle imeli sele e 9 .Fi 9 am Fig. 11 is a top plan viewof a yving f er a lfixed ine .a re ie o temp r r heliqe ters a e e relii el vrl w l ti cepecit fl er bqrsepqw r 'e u i .1 Ver low pay loads ascompared tojixeglyv ngairgraft. T fti ,szapeeit e l cop er i V ti f i tis not a unc o o in lmws ficient ,of the ,wings but glepends primarily;on a low magnitude; for the profile dr e- (Ibi invent o is l s W nesvlrrgharever .10w e a-e coefficients.

Maximum "lift vcc!efficients are significant ,for helicopter wings tosusta'm .the retreating wing and prevent vibration. lThisinvention'discloses slotted Wing sections .Whickprovide ,v ery;;high liftingcapacity for a very small amount ofpower to inducelflows through theslots to control the boundary layers.

Although these wines are especially useful, for .dirept.lift.aircraft,ytheyflareyalso'zvery "usefulfor The above" 51515055 areacqo mplished by the SFURES 'JWI LAYER Eflwarcl A. Stalker, Bay City,Mich.

if. 5, v li sm r 6 's'upborts the three blades I0 each suetiorislotsiintheiifsurfaes.' customer-yrs associate niairimum liftcoefficientshiith a preset butioii overT'the ear "the "leading vvardportion of erse' gradinfovr I I close's' a means ofobtainmgravoiaeie'gram ms aver the whole wing from leading to trailing'ags'wheri theviing" is operatingat maximum lift. I I ivhgil.a'f'wingflf Ffi'g. 3) is given a high archeanb'anibr line 12 sbrhat themaxidi'nate l abovethe sub- I 6 i'sfliar'g, "the pressuredistribulostantially the 'paar'nzo', 22, :24 sno s: It'will liebse'rvedthat the pressure 25 eri noises and .21 has every steep lose siat'izswith a r ve sal' orswpe "'ext e a' ilg" q er the ma or portion timedistanee b'ejt'weer'n' slots. described in my US.

i '.v l W answer w n section 4 h vin ejwn nuqqs r a ore e ent f t ress rWhi s? .L Aw r ififi e t ri e s c lihe pressure curve has a favorablegradient if the va ues 9 h mfluid essu x ec ne a one t e $11 l t m r9fiQW- Eben, t b u a y la r w pre'r' eq e rearwarci for long-distance ina laminar state. If there is a reversal in slope or gradient 9 th P T$1l 9l f e sh w get in F 3, the ibmllidary layer will become,turbulentland ;,l;hefdl'agfiwill be magnified several times at least.

It isja lso dlesirable'to have the gradient fairly uniform in value asshown bycurve M'fbetween slotsfifi-andffi .-In F-ig-.-;3 the curve 22might be raised to the ,dotted gurve 252a by vincreasing the suctionacting through'slot 5,2"! but the curve would still be unsatisfactory.ibecause itis still not everywhere steep enough to keep'the powerconsumption for the inductions 10w; glnffa'et'the raising of curve .22to 22a :by-power means obviously means more 3 power consumption. Howeverif the pressure curve 22 were raised by the proper arching of the wingcontour between slots, the slot flow power required would be low.

In Fig. 3 the segments 60 and 62 are convex arcs whose tangents atadjacent ends substantially coincide. That is the segments fair intoeach other to present a smooth convex contour to the upper surface ofthe wing.

In contrast in Fig. 4, the segment 64 has a concavity for a shortdistance aft of the slot succeeded by a relatively long convex length.This shape gives the curve M of substantially uniform favorable slope.

The aft portion of a surface is defined as convex if the centers for theradii of curvature always be on the side of the surface toward the bodyinterior. The forward portion of the surface is defined as concave onlyif said centers change sides with respect to said convex surface.

The segments 64 and 65 are respectively the upper portions of the flaps65 and 67. The segments are hinged to each other and to the main wingsection respectively, and suitable operating and adjusting means 63 areprovided as shown.

The segment 66 is similar to segment 63, but the segment 68 aft of slot10 is made concave throughout its length so that curve 48 just reachesfrom the stagnation pressure to about zero pressure at the trailingedge.

Fig. 5 shows the contour of the wing section when the flaps are raised.This is the low dra position and again the special contours are highlyadvantageous because they give more uniform gradients throughout thelength of the segment between slots. The pressure distribution curvesare 80, 82, 84 and 86.

The type of pressure distribution curve desired for the wing with flapsup is different than with flaps down. A steeper gradient is desirable inthe former case in order to assure maintenance of laminar flow in theboundary layer. In the latter case, that is with flaps down, a laminarflow is not desired. It is sufficient that the gradient be favorable orat least not greatly unfavorable so that the fiow will proceed rearwardwithout separating from the surface. A turbulent boundary layer is evenhelpful in preventing separation. By turbulent boundary layer is meantone in which mixing of the air particles is proceeding but there is noeddying such as accompanies separation.

With flaps down maximum lift is the main consideration and hence a largearea under the pressure curve is sought above the axis. This is achievedby having the pressure curve rather steep just aft of the slot. It istherefore necessary to compromise to some extent between the flap up andflap down conditions. Lowering the flap however tends to convert thetype of pressure curve for flap up to the type desired for flap down.

The flap or flaps are to be depressed until the maximum ordinate ofmeans camber line above its subtending chord is greater than 12% of thechord length. Even at a value less than 12% the flow will separate fromthe upper surface in the absence of boundary layer control as is wellknown in the science of aerodynamics. It therefore may be considered asdefining a lower boundary value above which boundary layer control isrequired to achieve increased lift from the greater arching of the meancamber line.

The pressure distribution curve over the fore part of the section can bemade more steep throughout its length by placing a slot 88 just aft ofthe nose, at about 20% of the chord. The section of Fig. 5 is shown inFig. 6 with such a nose slot. It now has the pressure curves 8! and 89and it will be observed that the curve 81 is steep throughout its lengthas compared to curve of Fig.5.

The contours between slots may be such that the steepest portion of thepressure distribution curve is at its aft end. This assures maintenanceof the laminar flow (flap up) for larger Reynolds numbers and in spiteof dirt or imperfections in the wing surface.

Fig. 7 shows the wing of Fig. 6 with nose and tail flaps depressed. Thepressure curves on the upper surface are 81a, 89a, 82a, 84a and 86a.

Fig. 8 shows the application of the special contour to a wing 96 with asingle flap 9% whose upper and lower surfaces are hinged at 99a.

In both Figs. 7 and 8 the lower surface of the rear flap is hinged tothe lower surface at 90 after the manner described in my U. S. PatentNo. 2,423,803, issued July 8, 1947, entitled High Lift Device.

In this type of flap the front edge of the upper surface of the flap isconstrained to slide on the surface it overlaps as the flap is lowered.Since the flap surface carries the concave-convex se ment the properfavorable gradient is assured over the flap surface.

Laminar flow is not maintained on a concave surface even by a favorablegradient for as great a distance as on a convex surface. It is thereforedesirable to keep the concave length short and convert to a convexlength in a short distance. Where a short concavity is succeeded by aconvexity the flow can be kept laminar. This requires at least two slotsand preferably three with the last one relatively close to the trailingedge.

Fig. 9 shows the application of the concaveconvex segments to a fuselage9|. This might also be a nacelle or any other body of the aircraft.

The fuselage is formed of the nose piece 92, and segments 95, 95, 96 and91. Between the segments are the induction slots I00 and H13. Theseslots extend transversely to the longitudinal axis and to the relativewind direction, preferably completely along the whole perimeter of thecross section.

The fuselage concave-convex segments insure pressure distributionsl29-I24 which are especially favorable to the maintenance of low drag oflaminar flow.

Fig. 11 shows the pumping means or blower I H) which is driven by themotor H2 to cause the boundary layer to be inducted through theslots ofan airplane wing I20.

It will now be clear that I have provided wings which have very highlifting capacity with a very small expenditure of power. This isachieved by forming the surface segments between slots with a specialcontour which gives a steeper, better distributed gradient betweenslots. Since these gradients are brought into existence by the geometryof the wing acting in conjunction with the relative wind, only a verysmall power is required from the pumping means for inducting air throughtheslots. It is to be noted that the flaps have the concave-convexcontour built into the flaps themselves.

When in the high speed condition the wings have a low drag because thefavorable properly distributed gradients of the pressure distribution:curvesse t eboundar layertflewicthe cond ion.

Whil I, "have .iuus ra e s ecific form o thi invent on sbe und rs cdth Iquot-inend to ml i myself in this exac form but ntend o I c aim minvention broadl a ind a ed by he ap ended: claims- :IcIa m :l. nrccmbiati nt for sb dy an afla slip portedinadiustab e r a on w t sai fla sbflow, .saidponcave-convexsurface cooperating with saidslot to provide acontinuously favorable pressure gradient thereacross, and means toinduce an inward "flow-of air through said slot.

2. in: combination, a-forabody and a flap sup ported: ad s a lrelation-with saidflap asu stantially in line chordwise with said forebody to form a wing adapted to be bathed by a relative flow of fluid,said flap having a chordwise extending upper surface contour which isconcave along its forward portion of short length and convex along itsaft portion of relatively greater length, the upper surface of said winghaving a slot ahead of said concave surface adjacent thereto, and meansto induce an inflow of air through said slot, said upper surface of saidflap overlapping the aft upper side of said body and presenting aleading edge to a rearwardly moving flow across the upper side of saidwing.

3. In combination in a wing adapted to be bathed by a flow of air, afore body and a flap supported in adjustable relationship with said flapsubstantially in line with said fore body, said flap being adjustable toa lowered high lift position to confer on said wing an airfoil sectionwhose maximum mean camber ordinate above the subtending chord issubstantially greater than 12 per cent of the said chord lengthwherefore said flow tends to separate from the upper surface of saidflap, said wing with flap depressed having an induction slot in itsupper surface leading into the wing interior, the forward portion ofsaid flap presenting a leading edge to said flow, means to induce a flowof the boundary layer air through said slot into said wing, the wingsection contour aft of said slot having a short concave length succeededby a relatively long convex length to provide a favorable pressuregradient aft of said slot of comparable magnitude along major portion ofsaid lengths when said fiap is in said lowered position.

4. In combination in a rotor for a direct lift aircraft, a hub structureadapted for rotation about an axis, a forward wing portion and arearward wing portion supported on said structure in spaced relation todefine a helicopter wing having a spanwise slot in the surface thereof,the segment of the surface adjacent the aft side of said slot having achordwise concave portion of short length succeeded chordwise by aconvex portion of relatively greater length, said concave portionoverlapping said forward wing portion and having a free leading edgedisposed thereabove providing a continuously favorable pressure gradientacross said concave and convex portions, and means to induce a flow ofair through said slot into the wing interior.

spaced slots teach having a t chordw said sla s-into he-W ne acre a; a puralit c ch ir tw n e ding int t e W211 segment t t fet endrh vin is, Incombination in a aster :fs direc .iit

hub str cture adapted f9;- ro tat' fstreams n ex po t n o re length, saic n av .ipp ti a n with said c n ex portion, exiea y a atelsucc ss ve so o the o her and 5P1?) continuou ly t meta ssur .sta sa d ,.c m.h nat or each sa portion c rl rp nd reward Wine and hav n :a free leading edispo above, and to induce aflowp I combination i .W .e ada te itcalving f ow o air f rm defining a plu a it (i i cave portion of shortlength succee by a chordwise convex portion of relatively greater lengthextending to the slot at the aft end thereof, said concave-convexsegment providing a continuously favorable pressure gradient thereacrossbetween successive said slots, and means to induce a flow of fluid intosaid wing interior through said slot, each said segment having a freeleading edge exposed to said flow.

'7. In combination in an aircraft body adapted to be bathed by arelative flow of fluid along the longitudinal direction thereof, aplurality of surface segments spaced apart in the longitudinal directionto form a plurality of spaced slots extending transversely to saidrelative flow direction, means to induce a flow of fluid inward throughsaid slots, each said segment presenting a leading edge to said flow,each said segment between slots having a longitudinally con-cavecurvature for a relatively short distance aft from its forward adjacentslot succeeded by a relatively long portion of chordwise convexcurvature extending to the rearward adjacent said slot, each saidconcave-convex segment in cooperation with said adjacent slots providinga pressure curve chordwise thereover having declining pressure valuesrearward therealong and being free of reversals of slope.

8. In combination in a wing adapted to be bathed by a flow of fluid, aforebody and a flap supported in adjustable relation with said flapsubstantially in line with said forebody, said flap being depressible toa lowered high lift position, said wing with said flap depressed havinga slot adjacent the upper aft end of said forebody, the upper surface ofsaid flap aft of said slot presenting a leading edge to said flow, saidflap upper surface having a short length of concave surface extendingrearward from said slot succeeded by a relatively longer length ofconvex surface, said lengths cooperating to provide a favorable pressurechordwise from said slot rearward over substantially the Whole combinedchordwise lengths of said concave and convex surfaces, and means toinduct fluid through said slots to cooperate with said lengths inproviding said favorable gradient chordwise over said flap.

9. In combination in a wing adapted to be bathed by a flow of air, aforebody and a flap supported in adjustable relationship with said flapsubstantially in line with said forebody, said two induction slots inits upper surface aft of the midpoint of the chord, and means to inducean inward fiow of boundary layer fluid into said wing, the segment ofthe wing section contour between successive said slots having a shortconcave length succeeded by a relatively longer convex length, each saidconcave-convex length cooperating with said slots adjacent thereto toprovide a pressure curve chordwise thereover having declining pressurevalues rearward therealong and being free of reversals of slope.

10. In combination in a wing for an aircraft adapted to be bathed by aflow of fluid thereacross, a forward wing portion, a rearward wingportion, means on said wing portions for supporting one upon the otherin spaced relation defining a spanwise slot therebetween in the surfaceof said wing, the segment of the wing surface adjacent the rearward sideof said slot having a chordwise concave portion of short lengthsucceeded chordwise by a convex portion of relatively greater length,said concave-convex segment providing a continuously favorable pressuregradient across'said portion rearwardly of said slot, said concavesegment at its forward end extending at least as far above the meancamber line as the rearward end of the forward wing portion adjacentthereto, and means to induce a flow of air through said slot into thewing interior.

EDWARD A. STALKER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,406,920 Stalker Sept. 3, 1946 2,408,632 Griffith Oct. 1,1946 2,438,254 stalker Mar. 23, 1948 2,447,100 Stalker Aug. 17, 1948FOREIGN PATENTS Number Country Date 483,497 Great Britain Apr. 21, 1938

